Wind turbines are machines containing a large number of mechanical components of various sorts that undergo constant stress. These components require regular maintenance usually entailing visual or physical access. The purpose of predictive maintenance is to determine the parts undergoing the most stress so as to reinforce them with a view to precluding failure and subsequent replacement of the component following its failure. This is of particular importance if the failure of the component entails the use of costly cranes to undertake the aforementioned replacement tasks.
The wind turbine hub houses the pitch system, comprising a hydraulic drive unit that moves a pusher shaft inside the hollow shaft. The pusher shaft in turns moves the star-shaped part, which transfers movement to the three blades. The joint between this hollow shaft and the flange supporting the pitch system bearing box is an element that undergoes an enormous amount of stress. Moreover, its position is hardly accessible, which consequently encumbers regular inspection and maintenance tasks. With a view to precluding issues concerning this joint and as a part of predictive maintenance, a new flange-based fastening system is proposed.
This flange has the main characteristic of being doubled, resulting in the following advantages:                The path of loads produced by the wind on the machine's pitch system is modified. This new reinforced flange renders better performance in terms of mechanical properties, as it is capable of transferring (through the reinforcement) greater moments and normal stresses by friction.        It is an accessible solution and can thus be inspected visually for subsequent maintenance.        It is easily mounted in the field with conventional tools (no need for hydraulic tools).        It does not depend on the condition of the star or hollow shaft, nor any adjustment between these elements. Should the machinery undergo some sort of failure affecting the bolts in the joint between the hollow shaft and the hollow shaft flange, but continue running despite the broken bolts in this joint, the resulting wear would entail a significant loss of material in the hollow shaft that would damage the internal geometry of the hole in the star. This could cause a loss in the adjustment between both elements, consequently increasing the frequency and amount of incidents of this failure. When mounting the joint reinforcement using the double flange, the worn spots on these elements do not intervene, hence the success of the solution is independent of the condition of the star and hollow shaft.        This solution is compatible with solutions that have been implemented previously in wind power farms comprising wind turbines, namely the reinforcement of the bolted joint by fitting shear pins between the hollow shaft and the star, the use of a key between the star and the hollow shaft, or the increase in the quality of the bolts constituting the joint itself.        